Method for making paper filled with alumino-silicate



United States Patent METHOD FOR MAKING PAPER FILLED WITH ALUMlNO-SILICATE Leon J. Paquin, Glens Falls, N. Y., assignor, by mesne assignments, to The Nationall'Cash Register Company, Dayton, Ohio, acorporation of Maryland No Drawing. Application November 6, 1950, Serial No. 194,386

3 Claims. (CL. 92-21) This invention relates to new and useful. improvements in methods for making filled paper, and particularly seeksto provide paper containing filler materials of such a nature that the formed paper sheets are capable of being used as sensitized record material ofthe type that produces a color reaction when subjected to printing or other type of character-forming operations with colorreactant materials.

Sensitized record materials to which this invention generally relates may be described as comprising a base sheet which carries a normally colorless reactant capable of reacting with a second, normally colorless reactant associated therewith whereby to cause the two reactant materials to produce color upon the practicing of any printing or other character-forming operations thereon.

This invention particularly provides a novel paper sheet for such sensitized record materials which has bodily incorporated therein as a filler certain materials which in themselves are normally colorless but which are capable of reacting with a second normally colorless material to produce color on the sheet as the direct result of' practicing printing or other character-forming operation thereon.

This invention also provides a novel method-for manufacturing the filled paper sheet in which the color-reactable filler materials are added to an aqueous pulp suspension prior to the time at which a sheet or web is formed'whereby to assure the even distribution of the filler materials and their reaction products throughout the finished'web and to coat the individual pulp fibers without causing the formation of-localized areas of solidified or fioccedv filler.

More-specifically, the sensitized paper sheet produced in accordance with this invention is particularly adapted for use in connection with organic color-reactable materials such as the phthalides disclosed in United States Letters Patent 2,505,470, granted to B. K. Green, April 26, 1950.

In the particular type of color. reaction in which paper made in accordance with this invention plays a part, fine particles of'solid inorganic material, providing a large adsorbent surface area, form one of two color reactants, and this material is adapted to cause a color change in certain organic compounds cominginto adsorption contact therewith. The organic compoundsmay be those disclosed in. the above mentionedpatent and.

may be used either in fluid or solid form, but if in solid form preferably should be carried in afiuid vehicle to promote the adsorption contact, and include such compounds as crystal violet lactone and. malachite green lactone. Crystal violetlactone is the 3,3 bis(p -dimethylaminophenyl) 6 ditnethylamino phthalide as disclosed in 2,757,085 Patented July 31, 1956 Tree i which the filler is incorporated into an aqueous pulp suspension prior to the time at which a web is formed.

A further object of this invention is to provide a method for making a filled paper sheet which comprises first forming an aqueous suspension of wood pulp, adding sodium aluminate to said suspension, then adding sodium silicate to said suspension and finally forming a paper web.

With these and other objects, the nature of which will become more apparent, a fuller understanding of this invention will be gained by reference to the following detailed description and the appended claims.

Heretofore other workers in the art have had some success in producing coated paper for use as the base sheets in sensitized color-producing record materials, but it has been considered impossible to employ filled sheets for thesame purpose in view of the fact that only a small fraction of the filler material would be available on the surface of the sheet for contact with the organic colorreactable material, whereas in the coated sheets a large part of the inorganic color-reactable material is available on the surface of the sheet.

For the first time this invention has solved the problem of how to make a filled sheet completely suitable for use as color-reactable sensitized record materials.

In accordance with the principles of this invention it (weight of bone-dry pulp per weight'of pulp and water) at ordinary temperatures was added 41 cc. of a freshly prepared 10% solution of sodium aluminate (15% by weight based on bone-dry pulp) with constant stirring. After the addition of the sodium aluminate was completed 41 cc. of a 10% solution of sodium silicate (15% by weight based on bone-dry pulp) was added with constant stirring. The resultant mixture was diluted with water to a volume of 2 liters in order to provide practical volumetric units when sheets are made. At this stage the pH values are generally on the order of 10 to 12. The mixture is then adjusted to a pH of 6.0 to 6.2 with a 10% solution of papermakers alum. Hand sheets were then made in a sheet'rnold, having a cross-sectional area of 31 sq. in. and a volumetric capacity in excess of 4 liters, by pouring a 50 cc. quantity of the above suspension into the mold in which there is sufiicient water to bring the volume to 4 liters, adjusting the pH to a value of about 6.0 by the addition of 0.08% alum solution, and then forming the sheet.

The resultant sheets of 31 sq. in. area each weighed about 0.9 gram (27.6 pounds on a 24 x 36-500 basis) and contained from 18% to 20% air-dry alumino-silicate filler. Each of these sheets when used with a second sheet coated with an emulsion containing malachite green lactone of the type disclosed in U. S. Patent 2,374,862 as an emulsion containing tetra-methyl-diamino-diphenyl phthalide, granted to B. K. Green on May 1, 1945, exhibited intense color and clear character formation when subjected to the action of a dry-faced adding machine printer or of a typewriter. A more specific formula for malachite green lactone is 3,3 bis (p-dimethylaminophenyl) phthalide. The malachite green lactone gives a green color when changed to its colored form. Other color reactants are suitable, such as crystal violet lactone, which has the formula 3,3 bis (p-dimethylaminophenyl)- 6-dimethylamino phthalide, which produces a dark blue color when changed to the colored form.

Example 2.Another 500 cc. of the same pulp suspension was treated exactly as in Example 1 above, but the pH in the sheet mold was adjusted to a value of about 5.0.

The resultant sheets contained from about 16% to 19% alumino-silicate filler. Each of these sheets when used with a second sheet coated with the emulsion coating containing malachite green lactone or crystal violet lactone exhibited a more intense color than that secured in Example 1 with the same clarity of character formation when subjected to the action of a dry-faced adding machine printer or of a typewriter.

In the foregoing examples the nature of the filler retained in the finished sheets was determined through the use of a pulpless system in which the quantities of chemicals, concentration of chemicals, successive dilutions and pH control were the same as for making handsheets. Thus 4.08 grams of air-dry sodium aluminate were dissolved in 40 cc. of hot water and added to 473 cc. of water. Then 40.8 cc. of the approximate composition Na2O-3.2SiO2 was added under continuous stirring to the sodium aluminate solution. The mixture was then diluted to a volume of 800 cc. and 95 cc. of a 10% alum solution was added to lower the pH from approximately 11 to 66.2. The mixture was then transferred to a 2-liter volumetric flask and made up to volume. Following this the mixture was poured into an open vessel and, while under constant stirring, a 100 cc. aliquot was withdrawn, diluted to 1 liter and filtered under vacuum on a tared #41 filter paper. Air-dry, bone-dry and ash weights were obtained on the residue. Gravimetric analysis indicated the alumino-silicate portion of the bone-dry filler to be of composition AlzOs-1.85SiOz-3.15Hz0. The air-dry (50% R. H. at 72 F.) filler contained 23% more free water.

It will be appreciated that other methods of analysis might produce different numerical results as to the amounts of retained filler in the finished sheets as well as variations in the indicated composition of the retained filler.

The foregoing two examples represent what now appears to be the optimum percentages of the added filler materials at pH values of 5 to 6 which are values that can be satisfactorily employed under standard mill procedures on full-scale runs.

It should be noted that within a wide range of total percentages of fillers used, based on pulp, a one to one ratio as between the sodium aluminate and the sodium silicate gives the best results with respect to color sensitivity of the finished sheet, but usable results as to color sensitivity are obtainable with the use of one part of sodium aluminate and from 0.7 to 2.0 parts of sodium silicate.

Surprisingly it has been found that to a considerable degree the color sensitivity and uniformity of these filled papers is dependent on the manner in which the filler compounds are added to the pulp suspension. It will be noted from the preceding examples that perfectly satisfactory results are obtainable when the sodium aluminate is added to the pulp suspension first followed by addition of the sodium silicate and pH adjustment with alum water. When this procedure is followed the individual fiber Of the pulp apparently become coated with the filler materials or the reaction products thereof and consequently the retained filler is uniformly distributed in fine particle form throughout the finished paper sheets.

However, when the order of addition of filler was reversed and the sodium silicate added first followed by the sodium aluminate the resultant paper sheets were not as satisfactory from the standpoint of color sensitivity. Similar troubles were encountered when attempts were made to form a clear fluid gel from the sodium aluminate and sodium silicate and then adding the gel to the pulp suspension.

In view of the fact that many variables will be encountered from time to time during the manufacture of filled color-sensitive papers of this type the quantities, consistencies, pH values, etc. given above should be rec ognized as illustrative only. Whenever changes are made in the specifications for the finished sheets in accordance with various end uses such changes invariably will require a change in the freeness of the pulp, for example, and a change in freeness in turn could well modify the amount of filler retained if the same gross amount of filler were added. Therefore, the quantities of sodium aluminate and sodium silicate would have to be changed from those given in the above examples in order to secure the same color sensitivity in the finished sheets. Similarly, variations in the nature of the wood pulp itself, for example use of a furnish of bleached sulphate pulp, or a mixture of bleached groundwood and sulphite pulps in place of all bleached sulphite stock will necessitate corresponding changes. In any event the correct amounts of the sodium aluminate and sodium silicate to be added will be for economical purposes the smallest amounts consistent with the obtaining of satisfactory color sensitivity in the finished paper.

In a machine run of paper made in accordance with this invention the filler materials are added to the pulp suspension at any convenient place in the system and the pH subsequently adjusted as in the foregoing examples. For illustrative purposes 15% by weight (based on bonedry, pulp) of the sodium aluminate solution may be added to the heater and followed by addition of 15% by weight (based on bone-dry pulp) of the sodium silicate solution. The pH adjustment to 6.06.2 through the use of alum is later made at any convenient place in the system between the heater and the paper machine, such as at a stock chest, regulator chest, fan pump or even at the paper machine head box.

I claim:

1. A method of making sensitized color-reactable paper comprising, forming an aqueous suspension of wood pulp, adding to said suspension a sufficient amount of sodium aluminate and sodium silicate that the finished sheet will contain not less than 16% air dry (50% relative humidity at 72 F.) alumino-silicate filler based on pulp, adjusting the pH of the resulting mixture to a value of 5-6, and thereafter forming a paper sheet.

2. A method of making sensitized color-reactable paper comprising, forming an aqueous suspension of wood pulp, adding to said suspension sodium aluminate, thereafter adding to said suspension sodium silicate, the total amount of the added materials being sufiicient to provide not less than 16% air dry (50% relative humidity at 72 F.) alumino-silicate filler based on pulp in the finished sheet, adjusting the pH of said pulp suspension to a value of 5-6, and finally forming a paper sheet.

3. A method of making sensitized color-reactable paper comprising, forming an aqueous suspension of wood pulp, adding to said pulp suspension sodium aluminate, thereafter adding to said suspension from 0.7 to 2.0 parts of sodium silicate for each part of sodium aluminate, the total amount of the added materials being sufiicient to provide not less than 16% air dry (50% relative humidity at 2 alumino-silicate filler based on pulp in the finished sheet, adjusting the pH of the resulting mixture to a value of 5-6, and finally forming a paper sheet.

References Cited in the file of this patent UNITED STATES PATENTS De Cew Apr. 15, 1919 Herting May 12, 1931 Rinrnan Sept. 27, 1932 Curtis Nov. 1, 1932 10 Weber Nov. 15, 1932 Hoskins July 27, 1937 Bjorksten Nov. 26, 1940 Baker Feb. 1, 1944 Gary Mar. 25, 1947 Harrison et a1 Apr. 11, 1950 6 2,550,467 Green et al. Apr. 24, 1951 2,550,470 Green et a1 Apr. 24, 1951 2,599,093 Craig June 3, 1952 OTHER REFERENCES 

1. A METHOD OF MAKING SENSITIZED COLOR-REACTABLE PAPERCOMPRISING, FORMING AN AQUEOUS SUSPENSION OF WOOD PULP, ADDING TO SAID SUSPENSION A SUFFICIENT AMOUNT OF SODIUM ALUMINATE AND SODIUM SILICATE THAT THE FINISHED SHEET WILL CONTAIN NOT LESS THAN 16% AIR DRY (50% RELATIVE HUMIDITY AT 72* F.) ALUMINO-SILICATE FILLER BASED ON PULP, ADJUSTING THE PH OF THE RESULTING MIXTURE TO A VALUE OF 5-6, AND THEREAFTER FORMING A PAPER SHEET. 